Compensating for non-linear thermal expansion when writing spiral tracks to a disk of a disk drive

Abstract

A method of writing spiral tracks for a disk drive is disclosed. A first concentric reference track is written at a first radial location near an outer diameter of a disk surface, a second concentric reference track is written at a second radial location near an inner diameter of the disk surface, and a third concentric reference track is written at a third radial location between the first and second radial locations. Prior to writing one of the spiral tracks, the concentric reference tracks are read to generate position error signals used to adjust a velocity profile for writing the spiral tracks. The velocity profile is adjusted to compensate for linear and non-linear disturbances due, for example, to thermal expansion.

Description

BACKGROUND[0001]1. Field[0002]The present invention relates to disk drives for computer systems. In particular, the present invention compensates for non-linear thermal expansion when writing spiral tracks to a disk of a disk drive.[0003]2. Description of the Related Art[0004]When manufacturing a disk drive, product servo sectors 20-2N are written to a disk 4 which define a plurality of radially-spaced, concentric servo tracks 6 as shown in the prior art disk format of FIG. 1. The product servo sectors are said to form servo wedges or servo spokes from the outer to inner diameter of the disk. Each product servo sector (e.g., servo sector 24) comprises a preamble 8 for synchronizing gain control and timing recovery, a sync mark 10 for synchronizing to a data field 12 comprising coarse head positioning information such as a track number, and servo bursts 14 which provide fine head positioning information. During normal operation, the servo bursts 14 are processed by the disk drive in ...

AI Technical Summary

Benefits of technology

[0011]In another embodiment, the velocity profile while writing the spiral track comprises a substantially sinusoidal component, and in one embodiment a magnitude of the sinusoidal component is based on a magnitude of the third position error signal. In one embodiment, the velocity profile while writing the spiral track compensates for a substantially sinusoidal position error between the rotational position of the actuator arm and the rotational position of the encoder.

Problems solved by technology

However, external servo writers are expensive and require a clean room environment so that a head positioning pin can be inserted into the head disk assembly (HDA) without contaminating the disk.

Thus, external servo writers have become an expensive bottleneck in the disk drive manufacturing process.

If the spiral tracks are written without compensating for this thermal expansion, the resulting non-uniform spacing between the spiral tracks may degrade and / or render the product servo sectors inoperable.

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